This is an important topic because a lot of machinery is designed to run on liquid fuels, and the energy:weight ratio in liquid fuel is extremely high.

My grandmother grew up in Normandy, France during WWII. It's known as cider country, and during the German occupation there was no fuel for the farm equipment so they would distill the cider to make high proof alcohol and run their machinery on that.

A still is dead simple to make, and even if you live somewhere where owning one is illegal, you can always have the prefabricated parts assembled and stored just in case.

Apples are a cold climate perennial food source. And a tree produces a lot of apples. I have an awesome processing system that I made on the cheap out of 5 gallon pails, some pallet wood, a hydraulic car jack, and a garbage disposal unit mounted into an old coffee table.

Granted, the disposal unit is electric, but the amount of work it does is phenomenal. I can process over 2 gallons of juice per hour on my own, and that includes the setup and cleanup.

Another liquid fuel can be fractionally distilled from wood. The process involves condensing the smoke out at various stages, and using catalytic materials to produce a range of gasses and liquid fuels that can be used around the homestead.

Here is a youtube vid of a guy making such a system in their backyard. Hi entire channel is worth browsing actually...